1. Field of the Invention
This invention generally relates to a method and system for power saving and state retention, and more specifically, to a method and system for power saving and state retention in an electronic device.
2. Description of Related Art
For modern portable electronic devices, such as portable multimedia players, mobile phones, and digital cameras, thin and light-weighted designs are essentially important while designing the portable electronic devices. Therefore, it is an important issue for the designers how to reduce power consumption. In a situation without an external power supply, lower power consumption also means longer usage time.
In order to save power, one of the common approaches is cutting off power on some inactive circuits of the electronic device. For instance, for a mobile phone with MP3 function, when the user is not using the MP3 function, the power supplied to the circuits in the mobile phone related to the MP3 function is temporary cut off. When the user uses the MP3 function, the power to the circuits related to the MP3 function is restored. The power of the mobile phone while user is not using the MP3 function is thereby saved, so as to achieve power-saving. The abovementioned power-saving circuit is designed generally similar to the power-saving circuit 10 shown in FIG. 1. The power-saving circuit 10 generally comprises a first circuit 12 and a second circuit 14. The first circuit 12 has a power control unit 16 and a state retention unit 18, wherein the power control unit 16 turns the power supplied to the second circuit 14 on/off according to the functional demand. At the time when the power supplied to the second circuit 14 is switched between on and off, the state retention unit 18 makes a backup of and restores states of a plurality of electronic components of the second circuit 14.
In general, the conventional power-saving circuit 10 can be classified into three types. The first type of power-saving circuit applies state retention flip flop in the second circuit 14 thereof. The state retention flip flop has a feature of maintaining its state at lower power, thereby achieving power-saving. However, the first type of power-saving circuit has disadvantages such as the request of a large area for circuit layout, particular rear end program support, incapability of making a backup of the information stored in the memory, and the request to make a backup of/restore states of all electronic components. The second type of power-saving circuit utilizes scan chain that is originally allocated for testing to backup and restore states of the second circuit 14. The disadvantages of the second type of power-saving circuit are slow speed while making backup/restoring states, request of particular rear end program support, incapability of making a backup of the information stored in the memory, and the request to make backup/restore states of all electronic components. The third type of power-saving circuit stores backup of the states of the electronic components in the memory by using existing bus and decoder. The third type of power-saving circuit has disadvantages such as consumption of time and power during the restoring process, and the request to make backup/restore states of all electronic components.